1. Field of the Invention
The present invention relates to an image forming apparatus of an electrophotographic system or of electrostatic recording system to be treated as, for example, a photocopier or a printer, etc.
2. Related Background Art
A color image forming apparatus adopting a so-called tandem system, which comprises a plurality of image forming stations (hereinafter referred to as xe2x80x9cstationxe2x80x9d) so that respective stations form toner images having respectively different colors and those toner images are superimposed sequentially and are transferring to forma color image, is conventionally known.
In each station described above, after a charging device has charged an image bearing member, the exposure of writing is executed corresponding to image signals with a semiconductor laser or an LED, etc. to form an electrostatic latent image onto the image bearing member, this electrostatic latent image is visualized as a toner image by developing means, and this toner image is transferred onto a recording material such as a transferring sheet or a film, etc. by a transfer device. In addition, the recording material after transferring is conveyed to a fixing device so that a toner image is fixed by the fixing device to give rise to the image.
In addition, in the recent image forming apparatus, those that are configured by using a belt running member such as a conveying belt being recording material bearing and conveying means for conveying a recording material to a plurality of stations in order to comply with full coloring and an increase in speed of the image forming apparatus are increasing in number. Otherwise, some are configured to sequentially transfer images in a plurality of stations onto an intermediate transfer belt as an intermediate transfer member to transfer the images onto the recording material. Various proposals have been made for a cleaning means to remove the toner attached to the surface of these belt members but it is well known that a cleaning blade, which is a plate-shaped cleaning member made of an elastic material such as rubber, etc. and has its edge brought into contact with the belt running member to scrape off and remove the attached toner, is already provided for practical use due to its simple configuration and high cost performance with good attached toner removing function.
Incidentally, in the color image forming apparatus configured as described above, long-term use of the apparatus is accompanied by NOx and toner resin, etc., for example, being attached onto the surface of the belt running member, and thus the surface friction coefficient of the belt running member rises up so that the friction force between the edge portion of the cleaning blade and the belt running member (the contact portion) will become large. Thereby, energy accumulated in the edge portion of the cleaning blade in a stick state will become large so that the Stick-Slip movement will be featured by the amplitude greater than a proper value and the frequency less than a proper value. Incidentally, the proper values are defined as a range in which a cleaning operation is executed stably.
Here, the Stick-Slip movement means the phenomena in which when the cleaning blade is brought into pressure contact with the surface of the belt running member with a force necessary to remove the residual toner on the surface of the belt running member, at first the edge portion tightly attached to the surface of the belt running member by the friction force applied to the contact portion undergoes deformation (slip deformation and compression deformation) in the travelling direction of the belt running member, and subsequently the energy accumulated in the edge portion accompanied by that stress functions as a force of restitution (impact resilience force) and gets back to the original state.
When these phenomena progress, the edge portion of the cleaning blade leaps up without following the surface of the belt running member, and passing-through of the toner or rubbing of the toner onto the surface of the belt running member (toner fusion bond and filming) takes place, and moreover, abnormal sounds (blade noise-making) and abnormal vibration (trembling) take place, a so-called blade turning up causing the edge portion to reverse so as to go along the direction of rotation of the belt running member takes place, or otherwise the edge portion or the surface of the belt running member could suffer from damages (chipping off in the blade edge or scratches on the surface of the belt running member).
In order to solve this problem, such measures are generally taken in which solid powder (lubricant) of inorganic substances such as graphite, boron nitride, molybdenum disulfide, tungsten disulfide, silicon dioxide, etc. and organic substances such as fluorine contained resin, silicone resin, polyamide (nylon resin), polyacetal, polyethylene, and polyimide, etc. are applied to the contact portion in which the edge portion of the cleaning blade is brought into contact with the belt running member so as to reduce the friction force.
However, since the lubricant will get lost from the edge portion of the cleaning blade due to long term use of the apparatus and the friction force will increase again, it will not be an essential key to reduce the friction force between the edge portion of the cleaning blade and the belt running member. In addition, to take these measures, a variety of apparatuses are used to supply the edge portion of the cleaning blade with the above described lubricant regularly, and as a result thereof, the configuration of the cleaning device will get complicated resulting in a significant cost increase.
In addition, as a method to plan reduction in the friction force between the cleaning blade and the belt running member, there is a method to use a cleaning blade in which a nylon resin layer is disposed on the contact surface with the belt running member (hereinafter referred to as xe2x80x9cnylon coat bladexe2x80x9d). In the case where this nylon coat blade is used, it is sufficiently possible to reduce the friction force between its edge portion and the belt running member.
However, unlike polyurethane, the nylon resin does not have properties as an elastomer, and does not show any function of removing the residual toner with Stick-Slip movement in the edge portion of the cleaning blade, but operates to clog the residual toner and to scrape off the residual toner and the like. Therefore, in order to completely prevent passing-through of the residual toner, it is necessary to increase the pressing force of the cleaning blade against the surface of the belt running member more considerably than in the case of polyurethane blade (approximately twice the polyurethane blade), and consequently inconveniences such as increase in abrasion wear in the surface of the belt running member due to cleaning blade or occurrences of scratches will take place, thus giving rise to such a problem that the life of the belt running member gets short takes place.
Under the circumstances, the present invention has been made in view of the above described problems, and the object thereof is to provide an image forming apparatus comprising a cleaning member that maintain good cleaning performance at a low cost even under a long-term use and can prevent abnormal sounds or abnormal vibration, and occurrence of turning up.
In order to attain the above described object, a first invention provides an image forming apparatus having:
a plurality of image bearing members which are disposed along the conveying direction of the transfer material and on which latent images are formed;
developing means which are disposed corresponding to the plurality of image bearing members and develope the latent images with a developer, respectively;
transfer material bearing and conveying means to bear and convey the transfer material;
transfer means to sequentially transfer the developer images developed on the plurality of image bearing members to the transfer material on the transfer material bearing and conveying means; and
a cleaning member which is brought into contact with the transfer material bearing and conveying means and cleans the surface of the transfer material bearing and conveying means,
wherein the developer image without undergoing transfer onto the transfer material is formed only onto an image bearing member disposed downstream-most in the movement direction of the transfer material bearing and conveying means among the plurality of image bearing members; and
the developer image is transferred onto the transfer material bearing and conveying means by the transfer means; and
the transfer material bearing and conveying means are moved so that the transferred developer image reaches the cleaning members.
In addition, a second invention to attain the above described object provides an image forming apparatus having:
a plurality of image bearing members which are disposed along the moving direction of the intermediate transfer means and on which a latent image is formed;
developing means which are disposed corresponding to the plurality of image bearing members and develop the latent images with a developer, respectively;
primary transfer means to sequentially transfer the developer images developed on the plurality of image bearing members to the intermediate transfer means;
secondary transfer means to transfer the developer images transferred onto the intermediate transfer means to a transfer material; and
a cleaning member which is brought into contact with the intermediate transfer means and cleans the surface of the intermediate transfer means,
wherein the developer image without undergoing transfer onto the transfer material is formed only onto an image bearing member disposed downstream-most in the movement direction of the intermediate transfer means among the plurality of image bearing members; and
the developer image is transferred onto the intermediate transfer means by the primary transfer means; and
the intermediate transfer means are moved so that the transferred developer image reaches the cleaning member.
According to the above described configuration, the developer image is formed only on the image bearing member disposed downstream-most among the plurality of image bearing members, and can supply the developer image to the cleaning member, and therefore, can maintain good cleaning performance saving the running cost by reducing useless consumption of the developer and can prevent abnormal sounds or abnormal vibration, and occurrence of turning up.